I am saying that I can't login from any account. Not just admin. As I said earlier after I log in. Its saying that I have successfully logged in but then its redirecting to the page where I am not logged in.

Okay, I also tried logging in to the admin panel through localhost/admin. After putting the id and password the Dashboard is showing but as soon as I click on anything such as the 'Check for Updates' or any other button (or option). It redirects back to the login page of admin which is localhost/admin.
Resolved it. The cookie path wasn't empty. It has to be set empty.